The function of a hot runner in an injection molding system is to contain and distribute molten, pressurized resin. Resin that escapes the distribution system flow paths can lead to system downtime, excessive maintenance and/or component failure and replacement. A challenge in the design of the distribution system is the management of the flow path connection between separate components.
A hot runner distribution system is typically comprised of several component types: a sprue to receive molten resin from the injection nozzle, a manifold to distribute the resin to several ports, and a plurality of nozzles to transfer the resin from the manifold ports to the receiving cavities in the mold. Each of these components may have a different material composition, due to desired thermal, strength, or wear characteristics. Different material types results in differing rates of thermal expansion for the components. This may be understood as relative motion between the components during the heat up and cool down phases of operation. High thermal conductivity is often a desirable trait for hot runner components. However, highly conductive materials tend to possess poor wear resistance. Relative motion between components may also occur during the assembly or maintenance periods.
Transfer of molten resin from one component to another is often achieved by seating the two components against each other and applying a sealing load. This load must be sufficient to resist the separation force generated by the resin pressure over the desired operational temperature range. However, an excessive load can damage the components and compromise the seal by creating surface damage that creates a resin leak path. Excessive load can also cause yielding of the components which can lead to component fracture and failure. The sealing load is often applied in the assembled or cold condition. This causes a load to be applied during the heat up and cool down phases that are periods of relative motion. Load combined with sliding contact increases the potential for surface damage of the sliding components. There may also be load applied during the assembly process.
Dissimilar material types, relative motion between components and high sealing loads contribute to the challenge of interface design. The following present invention describes an improvement in the design of hot runner component sealing interfaces that improves seal function while also allowing relative motion and the use of desired material types.
U.S. Pat. Nos. 5,299,928, 5,925,386, 6,164,954, 6,561,790, 6,609,902, 7,128,566, 7,137,807, 7,223,092, 7,507,081, 7,540,076, 7,549,855, 7,654,818, and U.S. Patent Publication No. 2004/0071817 disclose how thermal conductivities and/or wear resistant properties may be considered in a hot runner.